The present disclosure relates to a sheet detection device for detecting a sheet that passes through a sheet transport path, and an automatic document feeder and an image forming apparatus to which the foregoing sheet detection device is applied.
An image forming apparatus which forms, on a printing sheet, an image based on a document image on a document sheet includes a device body for performing image forming, and an automatic document feeder and an image reading unit. The document sheet that is set on a document tray of the automatic document feeder is transported toward the image reading position of the image reading unit, and the document image thereof is optically read. The device body includes an image forming unit for forming an image based on the image data of the document image. The printing sheet is transported via the image forming unit, and the image is transferred thereto when the printing sheet passes through the image forming unit.
As described above, in an image forming apparatus, a sheet transport path for transporting the document sheet or the printing sheet is essential. Disposed on this sheet transport path is a sheet detection device for detecting the pass-through timing of the sheet or a sheet jam on the sheet transport path. A photo interrupter is generally used as the foregoing sheet detection device. A photo interrupter includes an actuator in which a part thereof protrudes to the sheet transport path and which turns upon interfering with the sheet that passes through the sheet transport path, and detects a sheet based on whether the light path between the light emitting unit and the light receiving unit is blocked by the actuator.
When the sheet is transported in the forward direction of the sheet transport path, since the actuator interferes with the sheet and turns in a direction of retreating from the sheet transport path, the sheet can pass through with almost no resistance. Nevertheless, when a sheet jam occurs and the sheet is pulled out from the sheet transport path in a direction that is opposite to the forward direction, there are cases where the actuator pinches the sheet. In the foregoing case, the sheet is easily damaged.
Conventionally, known is an image forming apparatus using an actuator capable of protruding and retreating a part thereof. With this image forming apparatus, the part of the actuator is withdrawn from the sheet transport path in a state of being retreated into the actuator body in conjunction with the opening of the outer cover so that the removal of the sheet is facilitated during the occurrence of a sheet jam. Nevertheless, with this device, a link mechanism for protruding and retreating a part of the actuator in conjunction with the opening and closing operation of the outer cover is required, and which induces the increase in the number of components and the complication of the structure.
An object of the present disclosure is to provide a sheet detection device which will not obstruct the pull-out of the sheet from the sheet transport path without having to increase the number of components, and an automatic document feeder and an image forming apparatus to which the foregoing sheet detection device is applied.